Question 22

Question:

A 68 year old man with metastatic lung cancer is brought to the emergency room by his daughter, who reports that her father has been increasingly confused and lethargic over the past week. He denies any recent head trauma or any other medical problems. He reports taking chemotherapy but no other medications. On physical examination, his vital signs are stable, no jugular venous distention is present, and cardiac and lung exams are unremarkable. A CT scan does not show any brain metastases.
Laboratory results show:

Sodium: 124 mEq/L
Potassium: 4.6 mEq/L
Chloride: 102 mEq/L
Bicarbonate: 22 mEq/L

What is the most appropriate next step in managing this patient?

Correct Answer: E.  Restrict intake of water

This patient likely has Syndrome of Inappropriate Antidiuretic Hormone (SIADH), as a result of his lung cancer. He is hyponatremic, but euvolemic, as indicated by a normal jugular venous pressure and clear lungs. Other causes of euvolemic hyponatremia could be defects in glucocorticoid synthesis/release or hypothyroidism. In this patient, however, excess ADH secretion is likely, leading to the retention of free water and production of hyponatremia. The first step in management of SIADH is to restrict the intake of water, producing a gradual rise in serum sodium.